Revert "Follow-up to #13074: use spec syntax instead of deprecated mixins"
Revert "Follow-up to #13074: use spec syntax instead of deprecated mixins"

This reverts commit b10b373c6019666dbe1152245c9efdf214ceaa6a.

Resolves #14937.

ammula88/bootstrap,ammula88/bootstrap,ammula88/bootstrap,ammula88/bootstrap